Fluorinated esters of polycarboxylic acids



standing high temperatures.

United States Patent 3,096,363 FLUORINATED EST]??? 13F POLYCARBOXYLIC SEdward C. Ballard and Earl E. Summers, Wilmington,

DeL, assignors to E. I. du Pont de Nemours and Comparry, Wilmington,DeL, a corporation of Delaware N0 Drawing. Filed Dec. 8, 1960, Ser. No.74,449 10 Claims. (Cl. 260-468) This invention relates to novel estersof polycarboxylic acids and particularly to novel2-(lH,lH,wH-perfluoroallcoxy)ethanol esters of saturated polycarboxylicacids.

The rapid development of industrial technology and the advancement inthe design of jet engine aircraft have created a demand for stablelubricants and fluids for power and heat transmission which are capableof With- It is desired that such fluids be stable at temperatures of atleast 400 F. or higher, even as high as 600 F.; and form no sludge oncontinued use. it is further desired that such fluids have goodoxidative stability and low volatility.

Conventional fluids, such as the esterlubes and the petroleum oils, donot have satisfactory thermal and oxidative properties at temperaturesabove 300 F., while silicone oils gel at elevated temperatures. It isnow generally recognized that diba'sic acid esters of fluoro-alcohols asa class have better oxidative and thermal stability, as

well as lower flammability, than the conventional esterlubes andpetroleum oils. However, in general, they are too volatile for practicaluse in any but closed systems.

It is an object of this invention to provide new esters ofpolycarboxylic acids which have a novel combination of advantageousbeneficial properties, particularly having superior viscositycharacteristics and surprisingly low volatility characteristics. Anotherobject is to provide new esters of such character which are stable andwhich are useful as high temperature lubricants and as fluids tor thetransmission of heat and power. Other objects are to provide newcompositions of matter and to advance the art. Still other objects willappear hereinafter.

The above and other objects may be accomplished in accord with thisinvention which comprises the normally liquid esters of the iorrnulawherein R represents a saturated hydrocarbon radical of 2 to 20 carbonatoms having only one car-boxy group attached to any one carbon atom, mis an integer of 2 to 4, and n is an integer of l to 5. By normallyliquid is meant that the esters have a pour point of less than 100 F.

It has been found that the esters of this invention have a novelcombination of advantageous beneficial properties. They have improvedviscosity-temperature characteristics over those possessed by priorpolyfluoroalkyl esters of the corresponding acids. Particularly theyhave an extremely low volatility, materially lower than would heexpected from their molecular weight. In addition, they have excellentoxidative and thermal stability and are substantially noncorrosive tometals. Due to such combination of properties, they are especiallyuseful as high temperature lubricants and as fluids for the transmissionof heat and power. Particularly because of their low volatility, theyhave the advantage over the prior poly-fiuoroalkyl esters of thecorresponding acids of being useful as lubricants and as fluids for thetransmission of heat and power in open systems where evaporation is aproblem, as well as in closed systems.

The novel esters of this invention are the neutral esters derived fromsaturated polycarboxylic acids and 2-'(1'I-I,1vH,wH-perfluoroalkoxy)ethanols, which ester have the tormula wherein Rrepresents a saturated hydrocarbon radical of 2 to 20 carbon atomshaving only one canboxy group attached to any one carbon atom, m is aninteger of 2 to 4, and n is an integer of 1 to 5. Such esters includethe individual esters of a single polyfiuoroalkoxyethanol and a singlepolycarboxylic acid, the mixed esters of a mixture ofpoly-fluoroalkoxyethanols and a single polycarboxylic acid wherein twoor more of the alcoholic group of the ester are difierent in the valveof n, and mixtures of two or more of such esters.

The 2-(1H,lH,wH-perfluoroalkoxy)ethanols have the formula HO-CH CH O-CH(CF CF H wherein n is an integer of 1 to 5, preferably 2 to 4.Representative poly fluor oalkoxyethariols are 2-(lH,lH,3H-tetrafluoropropoxy) ethanol, 2-(1H,1H,5H-octafluoropentoxy)ethanol, 2-( 1H, lH,7H-dodecafl-uoroheptoxy)ethanol, 2-( 1H, 1H,9Hhexadecafluorononoxy)ethanol arid 2 (1H,1H, 1lH-eicosafluoroundecyloxy) ethanol.

Such polyiluoroalkoxyethanols of the present invention are the 1:1adducts of the corresponding fluorotelomer alcohols and ethylene oxide.The fluorotelomer alcohols and their preparation are described by R.M.Joyce in U.S. Patent 2,559,628. The fluorotelomer alcohols which areuseful fior preparingthe polyfluoroalhoxyethanols of this invention havethe formula I-I (CF CF ),,CH OH wherein n is an integer of 1 to 5,preferably 2 to 4, and mixtures of two or more thereof which areobtained by the process disclosed by Joyce. Representative fluorotelomeralcohols are:

The polyfluonoalkoxyethanols employed in this invention are readilyprepared by reacting the fluorotelomer alcohol or a mixture of two ormore theneof with ethylene oxide at elevated temperatures in thepresence of an alkali metal hydride or an alkali metal hydroxidecatalyst. The method of preparing the polyfluoroalkoxyethanols isillustrated by the following Example 1.

EXAMPLE 1 A solution of 15 grams of sodium hydride catalyst in 1020grams of 1H,1H,7H+clodecaliuoroheptyl alcohol was treated with ethyleneoxide in 140 C. to 150 C. until 148 grams had (been absorbed. Theproduct H-(OF CF CH OCH CH OH, was washed and distilled at C.- C. at 0.2mm. of mercury. Product analysis calculated as C H O 'F carbon 28.7;hydrogen 2.1; found carbon 28.3, 28.3 and hydrogen 2.2, 2.3.

By following the details of Example 1 using 59.2 g. of

3 50.6% sodium hydroxide, 2100 g. of 1H,1H,5H-octafluoropentyl alcohol(C absorbing 399 g. of ethylene oxide, yield of 1484 g. of the product,

mcn orp cn ocn cn on was obtained, boiling at 99 C.101.5 C. at 13-15 mm.of mercury.

All the fluorine-containing telomer alcohols heretofore mentioned can bereacted with ethylene oxide by following this procedure to form thecorresponding 1:1 adducts.

The polycarboxylic acids of this invention may be represented by theformula R(COOH) wherein R is a saturated hydrocarbon radical of 2 to 20carbon atoms, having only one carboxy group attached to any one carbonatom, and m represents an integer of 2 to 4, preferably 2 to 3. Thesaturated hydrocarbon radicals represented by R may be acyclic (openchain) or alicyclic (containing a carbocyclic ring), including alkylsubstituted carbocyclic hydrocarbons. Preferably, R will contain from 3to 8 carbon atoms and, in the case of the alicyclic hydrocarbonradicals, 6 to 8 carbon atoms. Representative saturated polycarboxylicacids which can be used to prepare the esters of this invention are:

Succinic acid Z-methyl succinic acid Glutaric acid Adipic acid 3-methylglutaric acid 3,3-dimethyl glutaric acid 2,2-dimethy1 glutaric acidPinic acid Pimelic acid Nor-camphoric acid 3-methyl-2-ethyl glutaricacid Suberic acid 1,4-dicarboxy cyclohexanoic acid Sebacic acidcamphoric acid 2,2,5,5-tetramethyl adipic acid 2,5-dicyclohexyl adipicacid Tricarballylic acid 3-methyl tricarballylic acid1,2,5-pentanetricarboxylic acid Camphoronic acid, and1,2,3,4-butanetetracarboxylic acid The esters are prepared from thepolyfluoroalkoxyethanol and the polycarboxylic acid according toconventional techniques. For example, the polycarboxylic acid or afunctional derivative thereof, preferably the anhydride, may be heatedin a hydrocarbon or halohydrocarbon solvent. An acid catalyst may beused. Normally, a strong acid cataylst is preferred, such as sulfuricacid, hydrochloric acid, p-toluene sulfonic acid, perfiuorobutyric acid,or mixtures of strong acids. The Water is removed as the solventrefluxes. The solvent and excess alcohol may be removed by vacuumdistillation, the residue cooled, washed with dilute alkali to removeany remaining acid present and the product purified by vacuumdistillation.

Alternately, the product need not be distilled from the reaction vessel,but can be purified by conventional techniques. For example, impuritiesmay be removed by solvent extraction, washing, adsorption on solidsubstrates, and the like. The product thus obtained is a clear,colorless or light yellow oil.

Mixtures of two or more of the polyfluoroalkoxyethanols can be reactedwith a polycarboxylic acid or with a mixture of two or more of thepolycarboxylic acids to provide mixed esters and mixtures of esters ofthis invention. Also, a single polyfluoroalkoxyethanol may'be reactedwith a mixture of two or more polycarboxylic acids to provide mixturesof esters of this invention. Such mixed esters and mixtures of esters,as well as mixtures obtained by mixing two or more individual esters,also have the advantageous benefical properties of the individual estersand are included within the scope of this invention.

In order to more clearly illustrate this invention, preferred modes ofcarrying it into effect and the advantageous results to be obtainedthereby, the following ex amples are given in which the parts are byweight, except where specifically indicated otherwise.

EXAMPLE 2 A mixture of 45.5 g. (0.25 mole) of camphoric anhydride, 188g. (0.50 mole) of 2-(1H,lH,7H-dodecafluoroheptoxy)ethanol, ml. oftoluene as reaction solvent and 1 ml. of concentrated sufuric acid ascatalyst was refluxed with continuous removal of water until no moreWater was formed. A total of 5 ml. of water was recovered. The mixturewas cooled, treated with 0.1 N aqueous KOH while stirring and the layersseparated. The crude ester was washed with'water, treated with 5 g. ofactivated alumina and 3 g. of activated charcoal, and the toluene andexcess alcohol were removed by stripping under vacuum. A final strippingaction was carried out at a pressure of 0.4 mm. of mercury while thetemperature was increased to C. C. When all evolution of vapors hadceased, the hot ester was filtered under suction through amedium-porosity sintered glass funnel giving g. (72% of theory) ofbis-[2-(1H,1H,7H-dodecafluoroheptoxy)ethyl]camphorate, a nearlycolorless oil, having a refractive index 11 of 1,3818, 1.3819 and adensity D of 1.5419. Analysis of the product as C H O F calculatedcarbon 36.7; hydrogen 3.06; fluorine 49.8; found carbon 36.6, 37.0;hydrogen 3.1, 2.9; fluorine 50.3, 50.5.

All the esters of this invention may be prepared by following thisprocedure.

EXAMPLE 3 When the details of Example 1 were repeated using a mixture of91 g. (0.5 mole) of camphoric anhydride, 304 g. (1.1 moles) of2(1H,1H,5H-octaflu0ropentoxy)ethanol and 200 ml. of toluene as reactionsolvent, 292 g. (75.4% of theory) ofbis-[2(1H,lH,5H-octafluoropentoxy)ethyl] camphorate, a clear amber oil,were obtained by vacuum stripping at 150 C. and 0.4 mm. mercury. The oilhad a refractive index n of 1.3961, 1.3961 and a density D of 1.4513.

EXAMPLE 4 When the details of Example 1 were repeated using a mixture of30 g. (0.1875 mole) of 3,3-dirnethy1g1utaric acid, 115 g. (0.417 mole)of 2-(1H,1H,5H-octafluoropentoxy) ethanol and 75 ml. of toluene asreaction solvent, 114 g. (94.5% of theory) of bis-[2-(1H,1H,5H-octafluoropentoxy)ethyl]3,3-dimethylglutarate, a colorless oil, wereobtained by vacuum stripping at 150 C. and less than 0.5 mm. mercury.The refractive index of the product was 11 1.3803, 1.3804 and itsdensity D was 1.4636.

EXAMPLE 5 are listed in Table I, in comparison with those of thecorresponding esters of unmodifiedfluorotelomer alcohols.

Table I Viscosity, es. Viscosity ASTM Volatility Ester Molecular IndexSlope (100- at 400 F., 1 Weight (ASTM 210 F.) percent in 210 F. 100 F.D567) 2111s.

Oamphorate of:

H(CF2CFz)zCHzOH 628 6. 50 80.1 -28 0. 888 100 H(VF:CF:)2CH2OGH:OHOH 7168. 94 109. 4 42 0.809 13 H(CF2CF2)3CHz0H 828 8. 20 113. 8 1 0. 858 65.H(CF2CF2)3CH:OCHCH2 OH. 916 10. 49 149. 6 34 0.809 93,3-Dimethylg1utarate of: H(CF CFq) CH2OH 788 3. 86 28.05 -'.46 0. 892100 H%OFCF2)2OH2OCH2CHOH 676 4. 71 33. 86 34 0.829 49 Trlcar allylateof:

H(CF2OF2)ZCH2OH 818 6. 64 76. 3 23 0. 867 27 H(OFrGFz)2CHzOOHgCHzOH 9509. 28 114. 1 46 0. 802' 8 The superior viscosity-temperaturecharacteristics of the esters of this invention are demonstrated by thelower ASTM slopes as compared with the corresponding esters of thefluorotelomer alcohols. Furthermore, the lower volatility of the estersof this invention is quite unexpected in comparison with that of thecorresponding esters of the fluorotelomer alcohols. Although it is to beexpected that the volatility would decrease as the molecular weight ofthe ester is increased, the magnitude of the decrease is far greaterthan could be expected. The additional molecular weight provided by theethylene oxide unit is only 44 for each polyfluoroalkyl chain. This isvery consider-ably less than that provided by the additional -CF CFunits required to produce the same reduction in volatility, each -CF CFunit increasing the molecular weight of each polyfluoroalkyl chain by100. As seen in the case of the camphorates, for example, the volatilityof the ester of H(CF CF CH OH is greater than 100% and the addition of a-CF CF unit, as in the ester of H(CF CF CH OH, reduces the volatility to65%. On the other hand, the addition of the ethylene oxide unit as inreduces the volatility to 13%.

The volatility of the esters was determined in fiat bottomed machinedaluminum test cups, W deep and 1%" inside diameter with ,4 thick wallsand bottoms, by the following procedure: The aluminum test cups wereweighed to 0.1 mg, about 2-3 grams of the oil sample were placedtherein, and the cups reweighed to 0.1 mg. The cups containing thesamples were placed on a hot plate, the temperature of which wasmaintained at 400 F.i F. At the end of the two-hour test period, thesamples were removed, the cups allowed to cool and then reweighed to 0.1mg. The sample weight loss was determined and is reported as percentevaporation.

The oxidative stability and simultaneous corrosive effect of the esterson metals were determined by the test method described by E. E. Sommersand B. M. Sturgis in US. Patent 2,840,593. The results are given in thefollowing Table II.

Table II OXIDATIVE STABILITY [500 132-24 hour test] V It will beunderstood that the preceding examples have been given for illustrativepurposes solely and that-this invention is not limited to the specificembodiments described therein. On the other hand, it will be readilyunderstood by those skilled .in the art that, subject to the limitationsset forth in the general description, other esters, mixed esters, andmixtures of esters of this invention can be prepared, without departingfrom the spirit or scope of this invention.

It will be apparent from the preceding description that the novel estersof this invention possess a novel, valuable combination of beneficialproperties, such as surprisingly low volatility, superiorviscosity-temperature characteristics, and excellent oxidativestability. These combinations of properties render such esters effectivefor the purpose of fulfilling the demand 'for stable, nonvolatile, hightemperature lubricants and fluids for transmission of heat and power inopen as well as closed systems. Accordingly, it will be apparent thatthis invention constitutes a valuable advance in and contribution to theart.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A normally liquid ester of the formula R [CO OCH CH --0CH CF CF H] mwherein R represents a saturated hydrocarbon radical of 2 to 20 carbonatoms, in which ester only one group is attached to any one carbon atomof R, m is an integer of 2 to 4 and n is an integer of 1 to 5.

2. A normally liquid camphoric acid diester of an alcohol of the formulawherein n is an integer of 2 to 4.

3. Bis [2-(1H,1H,7H dodecafluoroheptoxy)ethyl]- camphorate.

4. Bis [2 (1H,1H,5l-I-octafluoropentoxy)ethyl1-camphorate.

Final Viscosity Cu Total Acid Change, Evap. Ester Catalyst Sludge No.,Percent loss,

wt. loss, mg. g 1 mgJcrn. KOH/g.

Oamphorate of:

H(CFZCF2)2CH2OH 0.6 none 1.8 -4. 2 8. 2 H(CF;CF;)5OHOOHCH2OH.. 0. 8 none2. 5 2. 0 -6. 0 0. 10 H OFQCF2 3OH2OH 0. 4 none 1.4 4. 7 -12 0.09H(OF2OF2)3CH2OGHZCH2OH 1. 2 none 3. 4 +7. 4 +3. 2 0.14 3,S-Dlmethylglytarate of:

H(CF2CF2)3OH2OH 0.3 none 1. 4 1. 9 0. 8 0.05 H CFQCFQ)2OH2OCH2CH2OH 0. 6none 5. 8 2. 2 4. 4 0. 16 Tricar allylate of:

H (OFrCFmCHrOH 0. 3 cl udy. 1. 3 +2. 4 0. 03 H OF2CF2 2OH2O CHzCHaOH 0.5 trace 3. 6 -10 -20 0. 23

5. A normally liquid ester of the formula R[COO-CH CH -OCH(CFgCF L HJwherein R represents a saturated acyclic hydrocarbon radical of 3 to 5carbon atoms, in-Which ester only one group is attached to any onecarbon atom of R, and n is an integer of 2 to 4.

6. A normally liquid 3,3-dimethylglutaric acid diester of an alcohol ofthe formula HOCH CH -O-CH (CF CFQ H wherein n is an integer of 2 to 4.

7. Bis [2 (1H,1H,5H-octafluoropen-toxy)ethyl]-3,3- dimethylglutarate.

8. A normally liquid ester of the formula wherein R represents asaturated acyclic hydrocarbon radical of 3 to 5 carbon atoms, in whichester only one COO-CH CH OCH (CF CF H group is attached to any onecarbon atom of R, and n is an integer of 2 to 4.

9. A normally liquid tricarhallylic acid triester of an alcohol of theformula wherein n is an integer of 2 to 4.

10. Tris [2-( 1H,1H,5H-octafluoropentoxy) ethyl] -tricarballylate.

References Cited in the file of this patent

1. A NORMALLY LIQUID ESTER OF THE FORMULA